Research On Partial Discharge Ultrasonic Array Location Method In Transformer Based On Spatial Spectrum Estimation

Power transformer is a critical equipment in power systerm,and its operation reliability has a directly impact on the whole safety of power systerm. Partial discharge (PD)is a main reason of transformer insulation faults. PD locating detection is a key project in transformer insulation mechanism research and quality control. Emphasized much by the power depatment,it is an important foundation in tranformer's condition maintenance. The application of ultrasonic array location method for PD in trasformer can effectively improve the locating precision.Supported by the project of Chinese Universities Scientific Fund(No.09MG09) "Research on PD location of power transformer based on ultrsonic phased array" and Hebei Province Nature Scientific Fund, (No.E2010001703) "Research on PD location online of power transformer based on ultrsonic array sensors".In this paper, the ultrasonic array location methods of PD in transformer based on the spatial spectrum estimation are studied. And the main research acheivements are as follows:The direction of arrival (DOA) estimation algorithom of PD's narrowband signal based on Fast Direction Of Arrival (FastDOA) was presented. And the locating principles and usual algorithoms for PD's narrowband ultrasonic signal are stdudied.Model of narrowband array signal and sensors were built.Based on the algorithom of FastDOA, the DOA estimation of PD's narrowband array signal was simulated and compared with the simulation result estimated by using the algorithom of Root Multiple Signal Classification (Root-MUSIC).The result shows that the algorithom of FastDOA has a higher precision.The algorithom of focusing process based on RSS for PD's broadband ultrasonic array signal in transformer was presented.Here the necessity of the focusing process, as well as its principle and usual algorithoms for PD's broadband ultrasonic array signal were researched.Based on the algorithom of RSS, the focusing process and DOA estimation of PD's broadband ultrasonic array signal were simulated and compared with the simulation result by using the Consistent Focusing (CF) algorithom. The simulation results show that RSS has a better perfomance in focusing process.Based on multi-platform locating principle and global search with cloud optimazition,a novel method to locate the PD in transformer was presented. According to the direction angle and elevation angle of multiple locating lines and the known coordinates of sensors, the PD source was referred to the point from which the sum of distance in space to all the locating lines got the minmum value.Then global search the min-distance function with cloud optimazition algorithom to obtain the accurate geometric space coordinate of PD source.The simulation researches varify its correctness and feasibility.A whole set of ultrasonic array experimental systerm for PD location was built. The 4*4 platform ultrasonic sensors used in transformer's PD detection were designed and tested; a set of experimental platform of ultrasonic sensors, preamlifier,16 channles data collector and computer were also built; moreover, the soft systerm based on Lab VIEW for array location was established.Proceeding with large amount of experiments, array sensors' installation and the coupling test methods were studied. The results show the locating error is less than 10cm, and the location precision meets the requirements of practical projects.